pkgman: add command to show summary and description

Add command "info" to show the summary and description of a package
in a a remote repository.

Change-Id: I254eff3bb6401c90a394a483cd684134ead0a9a3
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6516
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>